1. Field of the Invention
The present system related in general to an engine for an outboard drive, and more particularly to a linkage system between charge formers of a marine engine.
2. Description of Related Art
A conventional internal combustion engine, which power an outboard drive, typically includes a plurality of charge formers to produce a fuel charge which is delivered to the combustion chambers of the engine. A throttle linkage commonly interconnects the charge formers to synchronize the operation of the charge formers and thus stabilize engine revolution. Other linkages, such as, for example, a choke linkage, may also interconnect other components (e.g., choke shafts) of the charge formers to synchronize the operation of those components.
Prior linkage designs for charge formers currently include a series of linkage rods which operate a plurality of levers. In the case of a throttle linkage, one end of a throttle lever is connected to a series of linkage rods and the other end is connected to a throttle shaft which operates a throttle valve. The throttle linkage typically includes a plurality of such levers which are placed in parallel to one another. The series of linkage rods operates the levers to control the positions of the throttle shaft.
With increased temperature, prior throttle linkage designs thermally expand which cause the positions of the throttle shafts and the corresponding throttle valves to become unsynchronized. For instance, where a linkage rod connects to a relatively fixed first throttle lever at one end and a movable second throttle lever at the other end, thermal expansion of the linkage rod will move the second lever relative to the first lever. The second lever therefore will no longer lie parallel to the first lever, and consequently the corresponding angle of the second throttle valve, which is operated by the second throttle lever, will differ from the angle of the first throttle valve. Thermal expansion of the linkage rod thus unsynchronizes the operation of the first and second throttle valves.
The prior arrangement of the linkage rods in a collinear series compounds this problem. The increased length of each throttle rod stacks up so that the lever operating the last throttle valve typically moves by an amount corresponding to the combined length increases of each throttle rod within the series. The angles of the first and last throttle valves thus can greatly differ so that the operation of the charge formers are no longer synchronized and engine revolution becomes unstabilized. When this occurs at a low revolutional speed (i.e., under idling conditions) the engine can stall.